Water Purification

Water Purification

Flooded area after a storm

After floods, storms, or disasters –– natural or manmade, or when camping, backpacking, fishing or on other outdoor adventures, access to safe, clean potable water is vital. Waterborne pathogens and harmful microbes like E. coli, rotaviruses, giardia, cholera salmonella and hepatitis A virus, render water unsafe to drink.

The dangers of unsafe drinking water cannot be overstated. It is estimated by to the World Health Organization that there is roughly 1.7 billion cases of diarrheal disease annually, out of which are the deaths of nearly 760,000 children under the age of five every year, the second leading cause of death in this age group.

Ironically, sunshine is an abundant source of energy, even in many of the most severely affected regions of diarrheal disease, that can not only cook food but can also heat water to temperatures that kill harmful microbes, making water safe to drink.

It has been known since the late 1880s when Louis Pasteur conducted groundbreaking research on bacteria, that heat can kill pathogenic (disease-causing) microbes.

The most foolproof method of water purification is by bringing it to a boil and keeping it roiling for at least one minute. At sea level water boils at 212° F. At higher elevations, however, water boils at lower temperature because of the reduction in air pressure which increases the boiling time. At altitudes above one mile, 2,000 meters, the roiling time should be at least three minutes.

Bringing water to a boil does use more fuel and reduces the water volume, as steam rising from the boiling water is lost water. You can literally boil a pot dry and lose all of your water, not to mention wasted fuel.

If biological contaminants are destroyed at a high temperature when heated for one minute, will exposing those same contaminants to lower temperatures for longer periods achieve the same results?

Contaminated water can be purified or pasteurized, the process of heating water to temperatures that kill these pathogens and harmful microbes, at temperatures well below boiling, as can milk, which is commonly pasteurized at 160 °F for 15 seconds.

Because the pasteurization temperature is much lower than the boiling temperature, pasteurization results in significant fuel savings when compared to boiling.

California State University at Sacramento researchers led by Dr. Bob Metcalf, emeritus professor in Microbiology and one of the original founders of Solar Cookers International (SCI), have proven that water need not be boiled to be pasteurized. Dr. Metcalf, known for his work on solar water pasteurization and solar cookers in many countries. has been able to confirm that contaminated water need only be heated to 150°F to make it safe to drink.

The table below shows temperatures at which the most common waterborne pathogens are rapidly killed. In one minute at least 90 percent of the microbes would be inactivated at the given temperature. After five minutes at these temperatures, there would be at least a 99.999 percent reduction in viable microbes capable of causing disease.

Microbes Killed Rapidly At…
Worms, Protozoa cysts (Giardia, Cryptosporidium, Entamoeba) 131°F (55°C)
Bacteria (Vibrio cholerae, E. coli, Shigella, Salmonella typhi), Rotavirus 140°F (60°C)
Hepatitis A virus 149°F (65°C)


Pasteurization is a viable and cost-saving alternative to boiling, though not foolproof — unless you know what the temperature of the water is.

The Water Pasteurization Indicator or WAPI was developed by North Star Devices to do just that. The SUPERWAPI with a tangle-free stainless steel cable highly resistant to heat was later offered to allow for use with fossil fuel as well as solar heat. Their latest variation the “floating” SPORTSWAPI II is available individually at solarsolutionscentral.com . Like the original WAPI, it is a clear 1-1/2” sealed clear polycarbonate cartridge with a small amount of specially formulated green wax at one end. The wax only melts at a certain temperature.

When the cartridge, tethered by the stainless steel cable, is vertically submerged in heated water, the wax at the top end will slide to the bottom end when the water reaches 150ºF. The water is heated long enough at a lower temperature to destroy the harmful microbes, and the melting process is a slow one so you know the water has been heated long enough at the lower temperatures to ensure safe drinking water.

After each use, to reset the wax to be ready for another, simply keep the cartridge vertical when cooling. For the next use, invert it with wax at the top of the cartridge, it is reusable over and over.

With the SPORTSWAPI II, the cartridge is held submerged coupled beneath its protective storage container which doubles as a “float”. Like the SUPERWAPI it is designed for use in solar and fossil fuel heated water.

Keep in mind when talking about water pasteurization it only refers to water biologically contaminated. Water with chemicals and other toxins cannot be made safe to drink through the pasteurization process.

Before pasteurizing, filter well, because debris floating in the water can have a negative effect on the process or at the very least let the debris settle before beginning.

Water placed in a glass or clear plastic container that is surrounded by reflective material is one way of pasteurizing water. You can cover the glass with black paint or black paper to enhance the process. This means that you can use a solar oven, stove, cooker or grill or some other means to pasteurize your water and know when the process is complete. Using a solar oven, stove, cooker or grill is ideal if it is such that you can place a container so it is heated using the reflective shields on the unit. Before buying a solar unit ensure you can pasteurize water if needed.